Need help with my registration page...

Requesting help on the coding and or construction of a checkbox that allows multiple options to be entered at once… for example, my website is sweathands.com It is a competitive gaming website for gamers to sign up for and meet other likewise players. I want to take down what platforms they use, and which games they play. So that means I need multiple options available for people who are registering to check, right now I can only figure out how to take down one value. I am no master coder, mostly just copy and paste. Any help would be greatly appreciated, even if its just a point in the right direction. Thanks.